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Understanding Synchronous vs Asynchronous

Before understanding AJAX, let’s understand classic web application model and ajax web application model first.

Synchronous (Classic Web-Application Model)

A synchronous request blocks the client until operation completes i.e. browser is unresponsive. In such case, javascript engine of the browser is blocked.

synchronous request

As you can see in the above image, full page is refreshed at request time and user is blocked until request completes.

Let's understand it another way.

how synchronous request works

Asynchronous (AJAX Web-Application Model)

An asynchronous request doesn’t block the client i.e. browser is responsive. At that time, user can perform another operations also. In such case, javascript engine of the browser is not blocked.

asynchronous request

As you can see in the above image, full page is not refreshed at request time and user gets response from the ajax engine.

Let's try to understand asynchronous communication by the image given below.

how asynchronous request works

Note: every blocking operation is not synchronous and every unblocking operation is not asynchronous.

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